The present capability of gun fire-control systems for point defense against antiship missiles is limited by normal gun system errors and the number of projectiles that can be fired during a short engagement. For this reason guided missiles are used as a defense against antiship missiles. However, the effectiveness of such guided missiles is limited to a minimum range of several miles. Furthermore, they can be used only on specially equipped missile ships. The employment of antiship missile systems aboard a ship requires that major and expensive modifications be made to the ship or that the ship be particularly designed for the missiles.
One way of avoiding these problems and requirements is to substitute for the fuze on standard gun-fired projectiles a unit to provide terminal guidance to such projectiles. Because of size limitations it is necessary to limit the size of the components within the terminal guidance system. Also, the environment necessitates a rugged design. Conventional target seekers are relatively large since they require gimbals and a reticle motor and are, therefore, unsatisfactory for this purpose. Also, they would not survive the 20,000 g's shock of being fired from a naval cannon.